复合函数z = g(f(x)),例如 f(x) = x+1 g(x) = x*x 计算其结果后,我想输出: g(x) = x*x,f(x) = x+1,g(f(2)) =9 怎么搞? 难道要将 “x*x”首先就作为字符串,编写解释器?